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no longer than 4000 feet (1219 m), 100 ohms maximum (Belden 9842 4-wire or 9841 2-wire, plenum
cabling Belden 88102, West Penn, or equivalent.) The drop cables (to readers and other devices) should be
kept as short as possible, no longer than 10 feet.
RS-485 Communications
The (EIA) Electronic Industries Association standard defines RS-485 as an electrical interface for multiport
communications on a bus transmission line. It allows for high-speed data transfer over extended distance
(4000 feet, 1219 m). The RS-485 interface uses a balance of differential transmitter/receiver to reject
common mode noise. For increased reliability over the extended distances End-of-line (EOL) termination is
required.
Belden (24 gauge wire – (7x32) Stranded Conductors – Polyethylene Insulated).
Belden Wire Specifications
Trade Number
Number
UL NEC Type
of Pairs
CSA
Certification
9841
1
NEC CM CSA
9842
2
NEC CM CSA
88102
2
NEC CMP CSA
Nominal
Shield
D.C. R.
Conductor
24.0 ohms/M
3.35 ohms/M
78.7 ohms/
11.0 ohms/K
km
24.0 ohms/M
2.2 ohms/M
78.7 ohms/
7.2 ohms/K
km
24.0 ohms/M
15.5 ohms/M
78.7 ohms/
50.9 ohms/km
km
Upstream Host Communication Wiring (Port 1)
TXD/TR1+
RXD/TR1-
RTS/R1 +
CTS/R1 -
GND
2-WIRE
PORT 1, CONFIGURED
Hardware Installation Guide
Nominal
Nominal Capacitance
Impedance
pF/feet
(Ohms)
120
12.8
120
12.8
100
12.95
revision 7 —
pF/meter
42
42
42
663
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